The marine mollusc Aplysia has been proven to be an extremely useful preparation for studying the cellular and molecular mechanisms of classical conditioning. We have recently discovered that Aplysia is also capable of exhibiting a reliabale form of operant conditioning: the animal rapidly learns to maintain a specific postural response in order to terminate the presentation of an aversive reinforcer (a bright light). Moreover, some of the elements in the neural circuit for the operant response are already known. Thus, it is the long term goal of this research project to analyze the cellular mechanisms of operant conditioning in Aplysia. There are two specific aims of the project: (1) a BEHAVIORAL ANALYSIS will be aimed at characterizing the detailed behavioral properties of the operant conditioning, including its basic and higher-order features; (2) a CELLULAR ANALYSIS will be aimed at specifying the neuronal mechanisms underlying the conditioning at progressively more fundamental levels, beginning with neural correlates in intact animals and progressing to directly producing the operant conditioning in both in vitro and analog systems, which permit detailed cellular investigation. Gaining insights into the cellular mechanisms of operant conditioning would be of significance from three perspectives: from a basic scientific perspective there is currently a real gap in our understanding of neuronal mechanisms of operant conditioning, even though it constitutes a significant form of associative learning; (2) from a theoretical perspective there has been a long-standing question in Psychology whether classical and operant conditioning represent two fundamentally different forms of learning. Since Aplysia now shows both forms of learning, a cellular analysis comparing their mechanisms could provide dey insights into this major theoretical question; and (3) from an applied perspective insights into cellular mechanisms of operant conditioning could potentially be of important clinical relevance. Since operant conditioning is routinely used in behavioral assessment of a wide variety of clinically relevant drugs, Aplysia could provide a powerful model system in which to explore the cellular actions of these drugs in mechanistic terms.